Bibliographic details of the publications referred to by author in this specification are collected alphabetically at the end of the description.
The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.
The frequency of atopy and the incidence of allergic diseases, such as seasonal rhinitis, have increased in recent decades, hereby making the characterisation of causative allergens a priority (Robinson et al. Linnenborg et al., 2001). Grass pollen, in particular, are linked to the onset of allergy in a very significant proportion of the population.
Bahia grass, Paspalum notatum, is endemic to sub-tropical parts of the Americas near the equator and has been introduced elsewhere, including Australia, as lawn, feed crop or under-planting ground cover in orchards (Firth). Bahia grass is a perennial warm weather bunch grass with a deep root system that grows well on all soils in wet areas. Production of pollen is moderate to heavy. Bahia grass pollen is capable of provoking an immediate hypersensitivity type I reaction in patients who are allergic to either this grass source or to pollen of Bermuda grass or other members of the subfamily Pooideae. Previous studies also indicate that patients allergic to the pollen of some trees also show strong reactivity to Bahia grass. Whilst the major temperate grass species including Timothy and Ryegrass pollinate during spring and early summer, triggering seasonal allergic rhinitis and asthma in sensitized individuals, the pollination period of Bahia grass extends from spring through to autumn, thereby often triggering allergic symptoms late in the grass pollen season. Accordingly, Bahia grass is recognised as an important allergen source for triggering allergic rhinitis and seasonal asthma (Davies et al., 2005; Weber et al. 2006).
To this end, the Group I allergens of grass pollen are important because they are clinically significant allergens which play a vital biological role in fertilization of the grass. They are major allergens which react at a frequency greater than 90% with serum IgE of allergic individuals. The Group I allergens generally comprise up to 4% of the total pollen protein, making them a major component of the pollen (Yennawar et al., 2006). However, they are critical not only because of their abundance but because of their function.
In terms of Bahia-related allergy, it has been reported that immunotherapy with a mixture of Timothy and Bermuda grass pollen extract could diminish wheals induced by allergen skin prick testing in response to 10 grasses including Bahia grass. It would suggest that inclusion of Bahia grass pollen may not be required for an effective grass pollen immunotherapy extract for seasonal allergy (Phillips et al., 1989). However, whereas Bahia grass is allergenic in nasal challenges, it is not cross reactive with Timothy grass pollen by nasal challenge, indicating that immunotherapy vaccines lacking Bahia grass may not effectively treat Bahia grass pollen allergy (Phillips et al., 1989).
Only limited IgE cross-reactivity between ryegrass and Bahia grass has been found, consistent with the distinct phylogeny of these grasses (Davies et al., 2005). Bahia grass is phylogenetically distinct from ryegrass and Timothy grass. While these two and other well characterised allergenic grass species belong to the Pooideae subfamily of temperate grasses, Bahia grass resides in the Pancoideae sub-family. Accordingly, despite the importance of Bahia protein as an allergen, the allergens of Bahia grass have not been characterised or defined. The availability of cloned individual allergens of Bahia grass pollen would facilitate investigation of IgE and T cell cross-reactivity, as well as providing reagents for component based immunology vaccines candidates for desensitisation of Bahia grass pollen allergy,
In work leading up to the present invention, the major Group I grass pollen allergen of Bahia grass has been identified, characterised and cloned. The identification of this allergen now facilitates the development of molecules and methods for the diagnosis and treatment of conditions such as those characterised by an aberrant, inappropriate or otherwise unwanted immune response to Bahia pollen.